Some recently-marketed information processors employ the magnetic recording/reproducing device. This recording/reproducing device operates in such a manner that after a disc (for example, a flexible magnetic disc) is attached to a spindle, this spindle is driven to rotate the disc. While it is rotated, a magnetic head is opposed to the recording surface of the disc to perform recording/reproducing of information.
The prior art will be described in detail with reference to FIG. 1 which is a sectional view of the conventional disc clamp device to be employed in the recording/reproducing device and FIG. 2 which is an enlarged sectional view of portion A of FIG. 1.
In this device, after a disc 2 is placed on a turntable 17 secured to a spindle 1, a frame 3 is moved down manually, for instance. On this frame 3 a shaft 4 is hung, a tapered face 11a of a hub 11 mounted rotatably on the lower end of the shaft 4 enters into a center hole 2a of the disc 2 in response to the downward movement of the frame 3. Then, the center hole 2a of the disc 2 moves in radial directions while being guided by the tapered face 11a to achieve the provisional centering action. At the same time, the hub 11 fits in a concave portion 17a formed in the turntable 17. Then, as the frame 3 moves down further, a collet 12 mounted on the shaft 4 via a bearing 13 and urged by a clamp spring 5 moves down into the hub 11. Because plural slits (not shown) are formed in the tapered face 11a of the hub 11, in response to the downward movement of the collet 12 the tapered face 11a is expanded, and the center hole 2a of the disc 2 is pushed in horizontal directions in the drawing, whereby the subject centering action is achieved. During the above operation, a pressing face 11b of the hub 11 pushes the disc 2 onto the upper surface of the turntable 17 to clamp the disc 2 thereon. The number 14 designates a return spring to return the collet 12 to its initial pose.
However, the conventional disc clamp device described hereinabove has the following problems:
(1) Because the centering action of the disc 2 relative to the spindle 1 is achieved through the indirect positioning function by means of the hub 11 and the collet 12, the degree of centering accuracy is limited to a certain extent. Accordingly, the conventional device is hardly applicable to the recently-developed high-density information recording system where a track pitch is narrowed. PA0 (2) Further, because both the clamping and centering actions of the disc 2 are performed by the hub 11, there is the probability that the clamping and centering actions would take place simultaneously or in the reverse order. In the above case, an unreasonable force is applied to the center hole of the disc and the disc is clamped before the accurate centering action is achieved. PA0 (3) If the pushing force of the collet 12 against the hub 11 is strengthened in order to assure the clamping of the disc 2, the pressing face 11b of the hub 11 inclines toward the bottom of the concave portion 17a of the turntable 17, as shown in FIG. 2. As a result, the clamping strength against the disc 2 becomes uncertain, the degree of centering accuracy lowers, and the disc 2 is damaged because of inclination of the pressing face 11b. PA0 (4) Furthermore, because the hub 11 and the collet 12 are independent members, the number of parts increases and the device structure becomes complicated. Correspondingly, the lowering of manufacturing efficiency and the cost-up of the device result.